The present invention relates in general to digital data switches and, more particularly, to a compact package for digital data switches operating with digital data signals up to and including gigabit and higher speed signals.
Packaging of digital data switches is an ongoing problem due, at least in part, to the electrical characteristics of the packaging materials which are used to mount a switch and associated control elements for the switch and to conduct data signals to and from the switch. For example, a digital data switch, typically one or more integrated circuit chips, is mounted on a printed circuit board (PCB) with electrically conducting traces formed on the switch board to conduct signals to and from the switch on the board. These traces present an impedance to signals which attenuate and can distort the signals. For high speed signals, the impedance and resulting attenuation and distortion can vary widely due to minor variations in the traces making signal retrieval difficult. Signals are also cross coupled among the traces and can be radiated from the traces leading to cross-talk among the signals and electromagnetic radiation or electromagnetic interference (EMI) which can cause operating problems for the switch and also for other nearby equipment.
In addition to the challenges presented by the switch board, signals to be switched are normally processed on secondary boards, for example port boards, which are commonly interconnected to the switch board by intermating electrical connectors. Even the best pairs of electrical connectors present an impedance mismatch when a port board connector is intermated with a switch board connector. As with trace impedances, connector impedance mismatches have significant effect on the attenuation and distortion of signals, particularly high speed signals.
Various approaches have been used in packaging high speed digital data switches. For example, attempts have been made to package the switch, associated switch circuitry and a plurality of port circuits on a common printed circuit board. While eliminating the expense and problems resulting from connectors, unfortunately such packaging results in very large boards with correspondingly long traces. These single board systems are difficult to maintain and are not well adapted to upgrades, particularly for the port circuitry.
In other configurations, port boards have been interconnected to both the front and back sides of a switch board. Unfortunately, such arrangements are more complex and result in larger switch package sizes.
In still other configurations, the port boards are reduced in size. While such reduced size port boards can result in compaction of a switch, for a switch accommodating a large number of ports, the trace lengths on the switch board still present a problem.
Accordingly, there is an ongoing need for improved packaging arrangements for high speed digital data switches operating with signals up to and including gigabit and higher speed signals. Preferably, such arrangements would be easily maintained and upgraded.